From If I Was The Evil Overlord:
Within my fortress, I will place a thick binder / CD / thumb drive / other data storage device where it can easily be found, and label it Operation Overlord SECRET PLANS. It will be booby-trapped. Many foolish short-sighted heroes will fall for this. For those who survive the experience, the contents will actually be a recipe book or something else innocuous. Heroes who are fully persuaded of their high intelligence will go crazy trying to figure out the secret code, which does not actually exist. (If they DO find a secret code, I will get them to show me what it is.)
My actual Secret Plans will be kept in my personal chambers and will be labelled something like Garbage Disposal Proposals.